The effect of doping the TiO2 lattice with copper was studied. TiO2-Cu semiconductors (0.1, 0.5, 1.0 and 5.0 Cu wt.%) were synthesized by the sol-gel method by incorporating Cu (NO3)(2) into the titanium alkoxide solution. In the samples thermally treated at 500 degrees C, mesoporous materials (9.5-12 nm) with specific surface areas of 90-52 m(2)/g were obtained. The X-ray diffraction (XRD) patterns of the annealed samples present anatase as the sole nanocrystalline phase (similar to 28 nm). The UV-vis diffuse reflectance spectra of the Cu-doped samples show a shift in the band gap to lower energy levels. The X-ray photoelectron spectroscopy (XPS) reveals a reduction in the oxidation state of the copper precursor, Cu(II), stabilizing Cu(0) and Cu(I) in the annealed solids. The photocatalytic test for the 2,4-dichlorophenoxyacetic acid degradation showed high efficiency and mineralization up to 92% (total organic carbon, TOC) in the Cu-doped sol-gel materials. The enhancement of the photocatalytic activity was discussed as an effect due to the Cu content as well as to the formation of stable Cu(I) in the Cu-doped TiO2 semiconductors. (C) 2009 Elsevier B.V. All rights reserved.